The temperature is dropping throughout the day as a cold front comes in. In City A, the temperature is changing by −5°F per hour, and in City B the temperature is changing by −3°F per hour. If the temperatures in both cities started at 70°F , which city is warmer, and what is the difference in their temperatures after 5 hours?
In City A, the temperature after 5 hours would be 70°F + (-5°F/hour * 5 hours) = 70°F + (-25°F) = 45°F.
In City B, the temperature after 5 hours would be 70°F + (-3°F/hour * 5 hours) = 70°F + (-15°F) = 55°F.
Therefore, City B is warmer than City A by 55°F - 45°F = <<55-45=10>>10°F. Answer: \boxed{10}.